1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3 .. _mem2mem: 4 5 ******************************** 6 Video Memory-To-Memory Interface 7 ******************************** 8 9 A V4L2 memory-to-memory device can compress, decompress, transform, or 10 otherwise convert video data from one format into another format, in memory. 11 Such memory-to-memory devices set the ``V4L2_CAP_VIDEO_M2M`` or 12 ``V4L2_CAP_VIDEO_M2M_MPLANE`` capability. Examples of memory-to-memory 13 devices are codecs, scalers, deinterlacers or format converters (i.e. 14 converting from YUV to RGB). 15 16 A memory-to-memory video node acts just like a normal video node, but it 17 supports both output (sending frames from memory to the hardware) 18 and capture (receiving the processed frames from the hardware into 19 memory) stream I/O. An application will have to setup the stream I/O for 20 both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` 21 for both capture and output to start the hardware. 22 23 Memory-to-memory devices function as a shared resource: you can 24 open the video node multiple times, each application setting up their 25 own properties that are local to the file handle, and each can use 26 it independently from the others. The driver will arbitrate access to 27 the hardware and reprogram it whenever another file handler gets access. 28 This is different from the usual video node behavior where the video 29 properties are global to the device (i.e. changing something through one 30 file handle is visible through another file handle). 31 32 One of the most common memory-to-memory device is the codec. Codecs 33 are more complicated than most and require additional setup for 34 their codec parameters. This is done through codec controls. 35 See :ref:`codec-controls`. More details on how to use codec memory-to-memory 36 devices are given in the following sections. 37 38 .. toctree:: 39 :maxdepth: 1 40 41 dev-decoder 42 dev-encoder 43 dev-stateless-decoder
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